Gastrointestinal problems are infrequent but serious complications of cardiac surgery, with high rates of morbidity and mortality. Predictors of these complications are not well developed, and the role of fundamental variables remains controversial. In a retrospective review of our cardiac surgery experience from July 1991 through December 1997 we found that postoperative gastrointestinal complications were diagnosed in 86 of 4,463 consecutive patients (1.9%). We categorized these 86 patients into 2 groups--Surgical and Medical--according to the method of treatment used for their complications. In the Medical group, 9 of 52 patients (17%) died; in the Surgical group, 17 of 34 (50%) died. By logistic multivariate analysis, we identified 8 parameters that predicted gastrointestinal complications: age greater than 70 years, duration of cardiopulmonary bypass, need for blood transfusions, reoperation, triple-vessel disease, New York Heart Association functional class IV, peripheral vascular disease, and congestive heart failure. Postoperative re-exploration for bleeding was a predictor specific to the Surgical group. Use of an intraaortic balloon pump was markedly higher in the Gastrointestinal group than in the Control group (30% vs 10%, respectively), as was the use of inotropic support in the immediate postoperative period (27% vs 5.6%). Our results suggest that intra-abdominal ischemic injury is a likely contributing factor in most gastrointestinal complications. In turn, the ischemia is probably caused by hypoperfusion due to low cardiac output, hypotension due to blood loss, and intra-abdominal atheroemboli. The derived models are useful for identifying patients whose risk of gastrointestinal complications after cardiac surgery may be reduced by clinical measures designed to counter these mechanisms.